The formulation of printing inks is dominated by the application for which the ink is to be used. Inks for gravure printing of paper or paperboard present a comparatively mild challenge to the artisan to formulate an appropriate ink but other applications can escalate that challenge beyond the scope of the state of the art. The required presentation of the printed article, the composition of the substrate on which the ink is to be printed and the post-printing process and use to which the article is to be exposed readily conspire to complicate the formulation process, often creating a need to formulate well beyond the state of the art. Metallized substrates, food packages and the packing process, laminates and the laminating process are just a few examples of specific end-uses or post-printing processes offering continuing challenges to the ink formulation artisan.
Known ink formulations are confronted constantly with the test to meet the needs of an ever changing mix of consumer products with ever changing print demands. Now, a fundamentally new constraint is being imposed upon many ink formulations by environmental regulations that urge a reduction in the use of organic solvents in ink formulations. For the more exacting applications such as inks suitable for laminates and the lamination process, the need to produce water based ink formulations which meet or preferably exceed the performance of formulations of laminating inks known in the art represents a prodigious challenge to the artisan. To this challenge, the present applicants have bent their efforts and provided the instant invention of a water based laminating ink formulation with performance properties that exceed those of the prior art.
Inks for lamination comprise a wide range of formulations depending upon the type of lamination process--adhesive, extrusion lamination or extrusion coating--the many substrates used, adhesive type and end-use of the laminate. In the foregoing laminates the printing ink is within the interface of the two substrates and the performance of the ink formulation must take into account and be compatible with the stresses of the lamination process. Key ink requirements are bond strength to the substrate and compatibility with the adhesive. Acrylic-based resins, among others, have been found to be useful as binders in meeting the formulation requirements of laminating inks. The physical mixture of styrenated acrylics and rosin esters as binders in flexible packaging inks is known to be particularly useful, but with limitations. They usually impart gloss and heat resistance to systems formulated with them. However, problems such as crinkle resistance, alcohol tolerance, bond strength and rheology can arise with their use.
U.S. Pat. No. 5,164,262 to Boswell, et al. discloses a method for the production of an acrylic polymer modified rosin ester binder for gravure printing ink formulations for paper. The binder is soluble in organic solvents such as toluene. U.S. Pat. No. 5,166,446 also to Boswell, et al. claims the acrylic polymer modified rosin ester. The Boswell, et al. patent is described hereinafter in greater detail with respect to the pertinency to the instant invention
U.S. Pat. No. 5,026,755 to Kveglis, et al. teaches a water-dispersable graft copolymer of a polyamide and an acrylic monomer produced by free radical polymerization.
U.S. Pat. No. 5,183,847 to El-Hefnawi, et al. discloses alkali soluble resins of carboxylated polyamide/acrylic resin prepared by a fusion process.
U.S. Pat. No. 5,216,064 to Rivera, et al. teaches rosin-based resin-fortified emulsion polymer compositions and the method for their preparation. The emulsions are prepared by polymerization of vinyl monomers and are used to prepare water based inks.
It is an objective of the present invention to provide a method for the production of a water soluble modified rosin-acrylic vehicle for laminating ink formulation.
Another objective of the invention is to provide a laminating ink exhibiting superior properties and containing the water soluble modified rosin-acrylic vehicle.